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 # Copyright (c) 2015-21, NVIDIA CORPORATION. All rights reserved.
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 # are met:
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 #    contributors may be used to endorse or promote products derived
 #    from this software without specific prior written permission.
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#pragma once
#include <deque>

namespace Falcor
{
    class FALCOR_API QueryHeap
    {
    public:
        using SharedPtr = std::shared_ptr<QueryHeap>;
        using ApiHandle = QueryHeapHandle;

        enum class Type
        {
            Timestamp,
            Occlusion,
            PipelineStats
        };

        static const uint32_t kInvalidIndex = 0xffffffff;

        /** Create a new query heap.
            \param[in] type Type of queries.
            \param[in] count Number of queries.
            \return New object, or throws an exception if creation failed.
        */
        static SharedPtr create(Type type, uint32_t count) { return SharedPtr(new QueryHeap(type, count)); }

        const ApiHandle& getApiHandle() const { return mApiHandle; }
        uint32_t getQueryCount() const { return mCount; }
        Type getType() const { return mType; }

        /** Allocates a new query.
            \return Query index, or kInvalidIndex if out of queries.
        */
        uint32_t allocate()
        {
            if (mFreeQueries.size())
            {
                uint32_t entry = mFreeQueries.front();
                mFreeQueries.pop_front();
                return entry;
            }
            if (mCurrentObject < mCount) return mCurrentObject++;
            else return kInvalidIndex;
        }

        void release(uint32_t entry)
        {
            assert(entry != kInvalidIndex),
            mFreeQueries.push_back(entry);
        }

    private:
        QueryHeap(Type type, uint32_t count);
        ApiHandle mApiHandle;
        uint32_t mCount = 0;
        uint32_t mCurrentObject = 0;
        std::deque<uint32_t> mFreeQueries;
        Type mType;
    };
}
